A computer program can be viewed as a detailed plan or procedure for solving a problem with a computer: an ordered sequence of computational instructions necessary to achieve such a solution. The distinction between computer programs and equipment is often made by referring to the former as software and the latter as hardware. An operating system (OS) is a set of programs that controls the interaction between applications and hardware. The OS also controls the interaction between different applications. The OS also provides generalized system services to application programs, such as utility and daemon programs. These system services conventionally include access to hardware peripheral devices attached directly or indirectly to the computer system. For example, the OS provides access to system hardware (e.g., by device drivers), and access to the file system on the hardware (e.g., by file system utilities.)
UNIX™, Windows™, and MacOS™ are examples of OSes. There are different varieties of UNIX™, such as FreeBSD™ and LINUX™, and different versions of Windows™, such as Microsoft's Windows NT™ and Windows 2000™. WindRiver's BSD/OS™ is a UNIX based OS derived from 4.4BSD Lite-1™. There are also different versions of MacOS™, such as MacOS 9.0™ and MacOS X™. Different OSes use different file systems for file access. For example, Windows NT™ uses Win32 file systems, such as FAT, or NTFS, while UNIX type systems use different types of file systems, such as UFS/FFS (UNIX File System and Fast File System) or ext2fs. UFS is a superset of FFS. UFS file system supports features that are not supported in Win32 file systems. Files types that are supported by the Win32 file system are referred to herein as “regular files”, whereas UNIX features or other files that are not supported by the Win32 file system are referred to herein as UNIX features and special UNIX files. For example, special UNIX files include hard links, soft links, FIFOs (First In First Out special file), named sockets and devices. UNIX features (also referred to herein as “characteristics”) include the access permissions, as well as ownership characteristics such as the owner (UID), and the group (GID) definition of a file.
Hard links are used to bind a file to a particular name in the file system. Symbolic links (e.g., soft links) are used to bind a particular file name to another file or directory name and may, for example, be used to by-pass some limitations of the hard links. A file or directory can be bound to more than one symbolic link. A FIFO allows data to be entered into a file and removed in the order that it was entered in. A FIFO may be opened by multiple processes for reading or writing. A device file allows an application to access a special hardware device of the computer. A named socket is used by processes of a same system to communicate. Each process can read/write information into a socket. Access permissions allow a user to designate, on a file by file or directory by directory basis, who has permission to read and write to a particular file or directory. The UNIX features (also referred to herein as “characteristics”) for the owner and group allow categorizing the access permission into three categories: the owner, the group and the others.
During development of an embedded application, it is often advantageous to use a target computing environment (e.g., a “target”) and a host computing environment (e.g., a “host”). The target is the device for which the application is being developed, and the host is used to develop the application for the target. In many circumstances, the target and host use different OSes (e.g., the host may run a Windows OS and the target may run a UNIX OS.)
Often, due to memory constraints, system administrative issues, or to simplify the development process, a process run on a target uses files stored on the host. Also, during the development process or the release process, it may be necessary to create on the host a file system for the target, i.e. a file system that the target OS can manage.
Sun Microsystem's NFS (Network File System) is an example of a software package that allows a target system to access files that are located on the host system. In NFS, files are loaded into the memory on the target as needed, so that there is no need to store the files on the target file system. To implement this, NFS mounts a directory on the target file system to a remote directory on the host. The host and target communicate in NFS via different commands set forth in the publicly available NFS protocol. As the host file system may not be able to handle all the file types or features of the target file system, such file types are located on the target file system.